The architect of post-9/11 New York City reveals the one move that changed the course of city history

Dan Doctoroff, now the head of Sidewalk Labs, pushed through major projects like the High Line and Hudson Yards when he was deputy mayor of New York City.

He says rezoning was a major driver of economic growth after September 11th.

In his new book, Doctoroff explains the choices he made that transformed the course of New York City history.

In the tech world, Dan Doctoroff is best known as the head of Sidewalk Labs, Alphabet's secretive urban innovation division that just announced a plan to build a new high-tech neighborhood in Toronto, Canada. There's perhaps nobody better suited to the task than Doctoroff, who led the huge post-September 11 transformation of New York City.

As the former deputy mayor of New York, Doctoroff pushed through projects like the High Line and Hudson Yards, rezoned huge swaths of the city, and seeded an economic resurgence that continues today. Co.Design calls him "the Chief Architect of 21st Century New York." It's not an exaggeration.

In his new book, Greater Than Ever: New York's Big Comeback, Doctoroff discusses his many successes and occasional failures (like a failed bid for the Olympics). But there's one move that Doctoroff and the Bloomberg administration made that changed the course of the city's history: rezoning almost half of New York City.

In the process, they not only changed the physical landscape of the city, but also paved the way for long-term economic growth — and the gentrification that goes along with it.

Zoning divides a city into districts that allow for different uses of property, like industry, housing, commercial, and so on. Changing zoning codes can have big impacts on a city's housing affordability, industrial practices, and overall economy. Prior to Bloomberg's tenure as mayor — which lasted from 2002 to 2013 — the last overhaul of New York City's zoning code happened in 1961.

Doctoroff told Business Insider that he didn't have one cohesive plan to rezone New York City. Instead, the administration undertook 140 separate rezoning actions. Each action took an individualized approach for a specific area.

"We knew we had to create a lot more land available for housing. Then we also knew we had to create business districts, and specifically mixed-use districts across the city to provide an array of choices for businesses that would want to either expand or locate here. Those two things were the pillars of our strategy," he said.

In some cases, this meant completely overhauling areas that had previously consisted of rotting piers and abandoned warehouses, as in the case of Hudson Yards and the waterfront areas in Greenpoint and Williamsburg, Brooklyn, according to Doctoroff.

"Now when you look at what's happening in Long Island City, Manhattan, downtown Brooklyn, it has validated the wisdom of some of those choices. I'm not saying we got it right 100% of the time, but when you look at the way the city has grown, I do feel we mostly got it right," he said.

Doctoroff acknowledged in the book that gentrification was a serious side effect of all this change. But he also defended it, saying that gentrifying neighborhoods prove the virtuous cycle of growth — more people moving in, more money raised for the city, more services offered — is working.

"When we first started, the truth is we weren't thinking about gentrification. It's important to remember, we started three and a half months after 9/11, when people on many levels were thinking about the validity of New York's model as an open city," he said.

"As a result, we embarked on this massive rezoning to create more capacity because we believed that [the city] was going to grow and that the mark of a successful city was growth. The place where we miscalculated is that at the end of the day the city grew much faster than we ever anticipated."

Zoning is a delicate balance: go overboard and you end up with a San Francisco-like situation, where building new housing is so difficult that the city starts to become unlivable. Allow lax zoning and you end up with what's happened in Houston, where sprawl takes over. Some people have recently argued that the hands-off zoning approach there also made the city extra-vulnerable to flooding.

Doctoroff's advice to other cities is to take a measured approach.

"Recognize that growth is good if it's properly managed. Too many cities, I think, take a reactionary approach to it," he said. "We were really proactive, but in retrospect, maybe not even proactive enough. Have faith in the future of your city."